At present, in the field of axial reciprocating axially moving hydraulic cylinders (including oil hydraulic cylinders, pneumatic cylinders, water hydraulic cylinders, etc.), the piston rod of the hydraulic cylinder is often inevitably exposed to dust, smoke, mist, steam, and harsh working environment such as gas, humidity, acid and alkali, heat, and severe cold. The dust, smoke, water vapor, and acid and alkali components in the environment enter the cylinder barrel of the hydraulic cylinder with the expansion and contraction of the hydraulic cylinder, contaminating the hydraulic fluid (oil, air or water, etc.) Moreover, when the hydraulic cylinder is operating, the temperature of the hydraulic fluid will change drastically, which will affect the physical and chemical properties (such as viscosity) of the hydraulic fluid. These combined effects will weaken the performance of the hydraulic cylinder, affects the working efficiency and quality of the hydraulic cylinder, and even causes malfunction of the hydraulic cylinder.